The present invention relates to an injector head for producing tread strips for tires, including a thickness-adjusting slide means and two side plates to form an essentially trapezoidal tread strip profile.
An injector head for producing tread strips and having adjustment capability for the tread strip profile has been known for a long time from U.S. Pat. No. 2,720,679. Such injector heads have a plurality of vertical slide means with which the thickness of the tread strip profile is supposed to be capable of being regulated at every point. In addition, this known construction provides a type of side gauge for adjusting the width of the tread strip profile, with the setting angle thereof additionally being adjustable, so that the extrusion angle of the sides or "wings", as they are also known, is adjustable.
This heretofore known injector head is not suitable for rapidly changing between different widths, as is necessary, for example, during the retreading of tires. In fact, a number of vertical slide means must be adjusted in order to be able to produce the new shape. The known construction is relatively expensive and susceptible to problems, and at the same time is not very precise, because the side gauges tend toward slight elastic deformations, depending upon the speed of extrusion. In addition, due to the side gauges, scrap rubber is always produced that can then be further processed only subsequently.
U.S. Pat. No. 3,870,453 furthermore discloses an injector head for producing tread strips that is characterized by a thickness-adjusting slide means that is adjustable in a single piece, and with which at the same time the width of the tread strip can be adjusted due to the essentially trapezoidal configuration of the tread strip profile, as well as the fact that the thickness-adjusting slide means is delivered from below, i.e. from the longer side of the trapezoid. However, this known injector head does not provide a fine adjustment capability, because the width and thickness of the tread strip profile are always simultaneously changed. Due to the enormous pressures in the chamber that is downstream from the extruder, a strong crossbeam is provided, and the thickness-adjusting slide means is supported by a special slide plate that can be swung away by a lever system if, for example, the injector head is to be cleaned. This heretofore known construction tends rather readily to tilt during displacement of the thickness-adjusting slide means. In addition, no possibility is provided for the coextrusion of bonding or carrier rubber.
In contrast, it is an object of the present invention to provide an injector head, for producing tread strips, of the aforementioned general type that combines great flexibility with a precise dimensioning of the tread strip profile, while at the same time being mechanically relatively inexpensive and uncomplicated.